System and method for drying green woods

ABSTRACT

A system for drying a large quantity of wood efficiently, which includes: a wood drying room capable of being sealed; a combustion-gas generator provided with an air-inlet conduit for introducing fresh air for combustion use into a combustion chamber provided in a lower area of the combustion-gas generator; a combustion-gas supplying passage extending from an upper area of the combustion-gas generator to an upper area of the wood drying room; an exhaust-gas discharging conduit extending from a bottom area of the wood drying room to a chimney; a combustion-gas recovery conduit extending from the bottom area of the wood drying room to the combustion-gas generator, and a gas flow-rate control unit provided in at least one of the exhaust-gas discharging conduit and the combustion-gas recovery conduit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for drying wood, and moreparticularly to a thermal dry stem for drying green wood, green bambooand other green plants (which have been harvested) to produce, in shortperiods of time, dried wood, dried bamboo and other dried plants whichhave been stabilized in their water content.

2. Description of the Prior Art

After harvest, green wood (and the like) are rich in water content, andusually carry many insects and their eggs. Consequently, in producinglumbers for building use and/or furniture use, it is usual to dry thegreen wood and chemically treat the same to kill the insects and theireggs.

In drying process, the green wood is hitherto subjected to naturalseasoning in which it is necessary to leave the green wood as it is fora long period of time, for example, three to five years in a wood yard.During this long period of time, it is necessary for workers of the woodyard to frequently move the wood to enhance the drying process thereof.However, leaving the wood for such long period of time in the wood yardresults in a poor investment, and is further disadvantageous inpreventing the woods from being attached by insect.

Under such circumstances, hitherto, various quick drying processes fordrying wood in short periods of time have been proposed. For example,one of these conventional drying processes is of a vacuum drying type.Another of these conventional drying processes is of a thermal heatingtype using a drying room to which hot air is supplied.

However, dried wood produced by conventional quick drying processessuffer disadvantages in that the wood is not prevented from cracking;and absorbing moisture which causes distortion of the woods, as in thecase of dried wood produced by natural seasoning.

In order to solve the above problems inherent in conventional quickdrying processes, another conventional process (i.e., a conventionalthermal heating type process) has been proposed. In the conventionalthermal heating type process, green wood is first housed in a dryingroom in which a hot combustion gas produced by burning waste wood andthe like is introduced so that the green wood is brought into contactwith the hot combustion gas so as to be dried and disinfected with heatand various smoke elements of the combustion gas to kill insects andtheir eggs in the woods, without being subjected to any chemicaltreatment, and without causing any distortion of the dried wood.

For example, Japanese Patent Laid-Open Nos. Sho 59-129373 and 60-103281disclose a conventional thermal heating type process in which green woodis housed in a treatment chamber which has: its upper area subjected toa hot blast; and its lower area subjected to a cool blast, so as to drythe wood. These Japanese Patent Laid-Open documents also disclose asystem for carrying out a process which is; however, poor in treatmentefficiency of the woods. In this process, when large quantity of greenwood is housed in the treatment chamber in order to improve thetreatment efficiency, the dried wood obtained through the process tendto vary in water content, which makes it impossible to stabilize theproducts (or dried wood) in quality.

SUMMARY OF THE INVENTION

In view of the above problems inherent in conventional drying processesand systems, the present invention was made.

Consequently, it is an object of the present invention to solve theabove problems by providing:

An apparatus for drying a large quantity of wood which comprises:

a wood drying room having a generally unrestricted open interior spacetherein and capable of being sealed;

a combustion-gas generator provided with an air-inlet conduit forintroducing fresh air for combustion use into a combustion chamberprovided in a lower area of the combustion-gas generator;

a combustion-gas supplying passage extending from an upper area of thecombustion-gas generator to an opening in the wood drying room whichopening is located at an upper portion of the wood drying room at oneside thereof;

an exhaust-gas discharging conduit extending to a chimney from a bottomarea of the wood drying room;

said chimney being located on a side of said wood drying room which isopposite said side at which said opening is located;

a combustion-gas recovery conduit extending from the bottom area of thewood drying room to the combustion-gas generator; and

a gas flow-rate control unit provided in at least one of the exhaust-gasdischarging conduit or the combustion-gas recovery conduit.

In the system of the present invention for drying the wood, thecombustion-gas recovery conduit may be directly connected with thecombustion-gas generator.

In the system of the present invention, it is also possible to connectthe combustion-gas recovery conduit with the air-inlet conduit.

Further, in the system of the present invention, the gas flow-ratecontrol unit (which is provided in at least one of the exhaust-gasdischarging conduit or the combustion-gas recovery conduit) ispreferably constructed of, in combination, a fan and a damper. Inaddition, it is also possible that the gas flow-rate control unit isconstructed of only one of the fan or the damper.

Furthermore, it is also preferable to provide a fan and/or a damper inthe air-inlet conduit of the system of the present invention. However,the provision of the air-inlet conduit is not indispensable to thesystem of the present invention.

In the system of the present invention, however, it is preferable toprovide a fan in at least one of the air-inlet conduit, exhaust-gasdischarging conduit, or the combustion-gas recovery conduit.

In operation of the system of the present invention having the aboveconstruction for drying the green wood and the like, waste wood and thelike are burned in the combustion-gas generator of the system to producea hot combustion gas accompanied with smoke. Then, the hot combustiongas is introduced into an upper area of the wood drying room through thecombustion-gas supplying passage.

In the wood drying room, the hot combustion gas passes through the greenwood (which is piled up in the room) downward to heat and dry the same,and reaches a bottom area of the room, from which bottom area thecombustion gas flows into the exhaust-gas discharging conduit and isdischarged to the atmosphere through the chimney of the system.

In the above operation of the system of the present invention, a part ofthe combustion gas flowing out of the bottom area of the wood dryingroom is circulated so as to enter the combustion-gas recovery conduitthrough which the thus circulated part of the combustion gas is returnedto the combustion-gas generator in which the thus circulated part of thecombustion gas is used to control a combustion speed of the fuel (i.e.,waste woods) in the generator in cooperation with a fresh air introducedinto the generator through the air-inlet conduit.

In an efficient drying operation of the green woods in the wood dryingsystem of the present invention, it is necessary for the system toproduce a combustion gas with substantially no oxygen content. Inaddition, it is not desirable for a temperature of the combustion gas toexcessively increase. Therefore, the circulation of the combustion gasin part is desirable in the system of the present invention. Bycirculating a part of the combustion gas through the system of thepresent invention, it is possible for the system to recover vapor andvolatile materials from the combustion gas before the gas is dischargedfrom the system through the chimney. The thus recovered volatilematerials are subjected to combustion again and burned in the systembefore they are discharged to the atmosphere through the chimney, whichcombustion contributes towards the solution of air pollution (caused bythe volatile materials contained in the combustion gas) and alsocontributes to cost saving since the volatile materials may be utilizedas fuels in the system of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows a longitudinal sectional view of the wood dryingsystem of the present invention, illustrating the construction of thesystem.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described in detail withreference to the accompanying drawing.

As shown in the drawing, in drying operation a of green wood (and thelike), the wood is housed and piled up in a wood drying room 1. The room1 is capable of being sealed, while so disposed as to be adjacent to acombustion-gas generator 2 an upper area of which is in communicationwith an upper area of the wood drying room 1 by means of acombustion-gas supplying passage 3.

A lower area of the combustion-gas generator 2 forms a combustionchamber 21 in which suitable fuels such as waste wood and the like areburned to produce a hot combustion gas. With the combustion chamber 21of the combustion-gas generator 2 is connected an air-inlet conduit 4for introducing fresh air into the combustion chamber 21.

Rotatably mounted in an opening-end portion of the air-inlet conduit 4is a damper 41 for controlling the flow rate of fresh air introducedinto the combustion chamber 21 of the combustion-gas generator 2.

At a plurality of bottom or floor positions of the wood drying room 1,the room 1 is connected with a plurality of combustion-gas recoveryconduits 5 to air-inlet conduit 4.

Mounted in each of the combustion-gas recovery conduits 5 are: a fan 51for sucking the combustion gas from the wood drying room 1 to supply thesame gas to the combustion-gas generator 2; and a damper 52 forcontrolling the flow rate of the thus sucked combustion gas from thewood drying room 1.

On the other band, an exhaust-gas discharging conduit 6 is connectedwith a corner portion of the wood drying room 1 so as to be oppositelydisposed from the combustion-gas supplying passage 3 in a diagonaldirection of the wood drying room 1, whereby an inlet portion of theexhaust-gas discharging conduit 6 is positioned at the remotest point ofthe wood drying room 1 with respect to the combustion-gas supplyingpassage 3. The exhaust-gas discharging conduit 6 extends to a chimney 7from which an exhaust gas passing through the conduit 6 is dischargedinto the atmosphere.

In the exhaust-gas discharging conduit is rotatably mounted a damper 61for controlling a flow rate of the exhaust gas to be discharged into thechimney 7.

In operation of the wood drying system of the present invention havingthe above construction, first, a suitable carrier such as a bogiecarries green wood to the wood drying room 1 in which the green wood ispiled up on the floor of the room 1. After that, the room 1 is closed soas to be hermetically sealed, and then a suitable fuel such as wastewood and the like is burned in the combustion chamber 21 of thecombustion-gas generator 2 to produce a hot combustion gas which flowsout of the generator 2 into the wood drying room 1 through thecombustion-gas supplying passage 3.

At this time, when the damper 61 of the exhaust-gas discharging conduit6 is closed, the hot combustion gas gradually fills the wood drying room1 and replaces air previously confined in the room 1, which air issucked into the combustion chamber 21 of the combustion-gas generator 2through the combustion-gas recovery conduits 5. Until the room 1 isfilled with the combustion gas, the thus produced hot combustion gas iscirculated through the system.

As the temperature of the wood drying room 1 increases with the heat ofthe hot combustion gas, the oxygen content of the atmosphere in the room1 decreases to lower the combustion speed of the fuel in the combustionchamber 21 of the combustion-gas generator 2, so that the rate oftemperature increases of the wood drying room 1 is lowered.

Under such circumstances, the damper 61 of the exhaust-gas dischargingconduit 6 is slightly opened to permit a part of the combustion gas(which is confined in the wood drying room 1) to escape to the chimney 7through the exhaust-gas discharging conduit 6. As a result, fresh air isintroduced into the combustion chamber 21 of the combustion-gasgenerator 2 through the air-inlet conduit 4, the amount of which freshair corresponds to that of the part of the combustion gas permitted toescape from the wood drying room 1. By controlling the amount of thefresh air introduced into the combustion chamber 21 of thecombustion-gas generator 2, the combustion speed of the fuel in thechamber 21 is adequately controlled.

In addition, in operation, by operating both of the fans 51 and thedampers 52 of the combustion-gas recovery conduits 5, a part of thecombustion gas confined in the wood drying room 1 is forcibly circulatedthrough the system so as to be supplied to the combustion chamber 21 ofthe combustion-gas generator 2, so that the fresh air supplied to thecombustion chamber 21 is diluted with the thus circulated part of thecombustion gas to make it possible to keep the oxygen content of theatmosphere in the wood drying room 1 low. As a result, in the system,the oxygen content of the atmosphere in the wood drying room 1 isprevented from varying, and the room 1 is also uniform or stabilized intemperature distribution.

As described above, in drying operation performed in the system of thepresent invention, the wood drying room 1 is filled with the hotcombustion gas which is low in oxygen content and stabilized intemperature distribution. Consequently, it is possible to effectivelydry the green wood in the wood drying room 1 of the system. The bulk ofvolatile gases produced from the green wood in the wood drying room 1during drying operation is so circulated as to be supplied to thecombustion chamber 21 of the combustion-gas generator 2, in whichchamber 21 these volatile gases are burned together with the fuel suchas waste wood to produce a combustion gas. Consequently, it is possiblefor the wood drying system of the present invention to prevent theatmosphere from being contaminated by such volatile gases.

Incidentally, in the above embodiment of the system of the presentinvention, the exhaust-gas discharging conduit 6 is directly connectedwith the bottom corner portion of the or wood drying room 1. However, itis also possible for the system of the present invention to permit apart of the exhaust-gas discharging conduit 6 to form the combustion-gasrecovery conduits 5.

Further, in the wood drying system of the present invention, it is alsopossible to form the exhaust-gas discharging conduit 6 as a branchedconduit of any one of the combustion-gas recovery conduits 5.

Still further, in the wood drying system-of the present invention, thegas flow-rate control unit is constructed of: the fans 51 and thedampers 52 combined with the fans 51; or the damper 41, 61 only.However, it is also possible to replace such gas flow-rate control unitwith a speed-controllable fan capable of being controlled in rotationalspeed.

In wood drying system of the present invention, since the hot atmospherein the wood drying room 1 is kept low in oxygen content while beinguniform or stabilized in temperature distribution, it is possible toproduce the high-quality products or dried woods with good yields.

What is claimed is:
 1. An apparatus for drying a quantity of wood whichcomprises:a wood drying room which includes a plurality of walls havingexterior surfaces, which walls define a generally unobstructed openinterior space and a combustion-gas supply passage therebetween whichare capable of being sealed; a combustion-gas generator provided with anair-inlet conduit for introducing fresh air for combustion use into acombustion chamber provided in a lower area of said combustion-gasgenerator, said combustion-gas supplying passage extending from an upperarea of said combustion-gas generator to an opening in said wood dryingroom which opening is located at an upper portion of said wood dryingroom at one side thereof; an exhaust-gas discharging conduit extendingto a chimney from a bottom area of said wood drying room, said chimneybeing located on a side of said wood drying room which is opposite saidside at which said opening is located; a combustion-gas recovery conduitextending from said bottom area of said wood drying room to saidcombustion-gas generator; and a gas flow-rate control unit provided inat least one of said exhaust-gas discharging .[.control.]. .Iadd.conduit.Iaddend.or said combustion-gas recovery conduit, wherein said generallyunobstructed open interior space is rectangular.
 2. An apparatus fordrying wood, as set forth in claim 1, where:said combustion-gas recoveryconduit is directly connected with said combustion-gas generator.
 3. Anapparatus for drying wood, as set forth in claim 1, where:saidcombustion-gas recovery conduit is connected with said air-inletconduit.
 4. An apparatus for drying wood, as set forth in claim 1,where:said gas flow-rate control unit comprises a fan and a damper. 5.An apparatus for drying wood, as set forth in claim 1, where:said gasflow-rate control unit comprises at least one of a fan or a damper. 6.An apparatus for drying wood, as set forth in claim 5, where:said fan orsaid damper is provided in said air-inlet conduit.
 7. An apparatus fordrying wood, as set forth in claim 5, where:said fan is provided in atleast one of said air-inlet conduit, said exhaust-gas dischargingconduit, or said combustion-gas recovery conduit.
 8. An apparatus fordrying wood, as set forth in claim 1, where:said gas flow-rate controlunit comprises a speed-controllable fan.
 9. An apparatus for drying aquantity of wood which comprises:a wood drying room which includes aplurality of walls having exterior surfaces, which walls define agenerally unobstructed open interior space and a combustion-gas supplypassage therebetween which are capable of being sealed; a combustion-gasgenerator provided with an air-inlet conduit for introducing fresh airfor combustion use into a combustion chamber provided in a lower area ofsaid combustion-gas generator, said combustion-gas supplying passageextending from an upper area of said combustion-gas generator to anopening in said wood drying room which opening is located at an upperportion of said wood drying room at one side thereof; an exhaust-gasdischarging conduit extending to a chimney from a bottom area of saidwood drying room, said chimney being located on a side of said wooddrying room which is opposite said side at which said opening islocated; a combustion-gas recovery conduit extending from said bottomarea of said wood drying room to said combustion-gas generator; and agas flow-rate control unit provided in at least one of said exhaust-gasdischarging control or said combustion-gas recovery conduit, whereinsaid combustion-gas recovery conduit comprises a manifold havingconduits extending from a plurality of positions in said bottom area ofsaid wood drying room and wherein said gas flow-rate control unit isprovided in each of the conduits and selectively operable to open orclose each respective conduit.
 10. An apparatus for drying wood as setforth in claim 9, wherein said manifold conduits are provided through abottom surface of said wood drying room. .Iadd.
 11. A method of dryingwood which comprises:piling green wood in a drying room; closing andhermetically sealing the drying room; producing a hot combustion gas ina combustion chamber; introducing said hot combustion gas from thecombustion chamber into the closed and hermetically sealed drying roomso as to gradually replace air previously confined in the drying room,until the drying room is filled with said hot combustion gas; andcontrolling a combustion rate in the combustion chamber after the dryingroom is filled with said hot combustion gas by controlling an amount offresh air introduced into the combustion chamber and by allowing anequivalent amount of said hot combustion gas to escape out of the dryingroom and by forcibly circulating a portion of said hot combustion gas soas to keep the oxygen concentration in the drying room at a constantlevel and to stabilize temperature distribution in the drying room..Iaddend..Iadd.12. A method for drying wood according to claim 11,wherein said hot combustion gas is produced by burning wood in thecombustion chamber. .Iaddend.